If a birefringence medium causing a light polarized by passing a first polarizing means to have different polarization directions according to wavelengths is arranged between the first polarizing means and a second polarizing means and a light is emitted to transmit through them in sequence, the light out through the second polarizing means presents color.
The present inventors have invented various display or illumination devices by using these phenomena and the inventions have been filed with Korean Patent Application Nos. 10-2012-0070627 (title of the invention: Polarization display device in which color and shape can be changeably viewed according to position of view), 10-2012-0070519 (title of the invention: Color change device by means of polarization) and 10-2011-0124247 (title of the invention: Polarization illumination system) so on.
In generating color by means of polarization of light in the field of the illumination or display, it is desirable if it is possible to generate various colors and chroma of the generated colors is high. For example, if a color-generation device is applied to an advertisement sign, it will attract more persons and achieve more advertisement effect as the chroma is getting higher and more various colors are getting generated.
The present inventors have tried their best efforts to develop an illumination or display device which generates color by means of polarization of light and to improve the quality of the generated color, and have filed Korean Patent Application No. 10-2013-0055010 (Title of the invention: Color-generation apparatus by means of polarization of light for generating color having high chroma or high concentration). This invention improves concentration or chroma of the generated color by arranging three polarizing means and, at least, two birefringence media.
The present inventors have found that, as for the light (visible light) entering the polarizing means at which color is to be generated after being polarized and passing through the birefringence medium, if the polarization states in the light according to the wavelengths are linear polarizations or even elliptical polarizations having high tendency of linear-polarization, it is helpful to generate the improved color. Whereas it is not helpful to generate the improved color if they are either circular polarizations or elliptical polarizations near to the circular polarizations. Accordingly, if it is possible to make the polarization states of the light according to the wavelengths have more linear polarizations or tendency of linear polarization higher and if it is possible to make the directions of the linear polarizations according to the wavelengths more different from one another, it is possible to generate more various colors and the generated color will be more improved.
Here, for instance, if the circular polarization state is put at one extreme and the linear polarization state is put at the other extreme, then, the states between the two extremes indicates elliptical polarization. The oscillation state becomes to be more linear towards the linear polarization state from the circular polarization state and it is said that the tendency of linear polarization is getting higher towards the linear polarization state from the circular polarization state.
Assuming that waves of two colors in the visible light are in the linear polarization states, if the directions of the polarizations of them are the same or are a little different even though they are not the same, the two colors according to the waves are mixed and it is difficult to generate the improved color. If the different colors according to the different wavelengths are in the linear polarization states, it is more helpful to improve the chroma and generate various colors as the polarization directions of them are more different from one another.
In this specification, description that “the tendency of linear-polarization of a light is increased” or “increase the tendency of linear polarization of a light” means to make the polarization states of the light according to wavelengths have higher tendency of linear-polarization according to wavelengths in overall and make the polarization directions according to wavelengths more different from one another.
The present inventors have tried to find a way to increase such a tendency of linear polarization of a light and the present invention is the result.